Mediators of Bradykinin-Induced Vasorelaxation in Human Coronary Microarteries

Abstract

Abstract-To investigate the mediators of bradykinin-induced vasorelaxation in human coronary microarteries (HCMAs), HCMAs (diameter Ϸ300 m) obtained from 42 heart valve donors (20 men and 22 women; age range, 3 to 65 years; mean age, 46 years) were mounted in Mulvany myographs. In the presence of the cyclooxygenase inhibitor indomethacin, bradykinin relaxed preconstricted HCMAs in a concentration-dependent manner. N G -nitro-L-arginine methyl ester and ODQ (inhibitors of nitric oxide [NO] synthase and guanylyl cyclase, respectively) and the NO scavenger hydroxocobalamin, either alone or in combination, shifted the bradykinin concentration-response curve to the right. Removal of H 2 O 2 (with catalase), inhibition of cytochrome P450 epoxygenase (with sulfaphenazole or clotrimazole) or gap junctions (with 18␣-glycyrrhetinic acid or carbenoxolone), and blockade of large-(BK Ca ) and small-(SK Ca ) conductance Ca 2ϩ -dependent K ϩ channels (with iberiotoxin and apamin), either alone or in addition to hydroxocobalamin, did not affect bradykinin. In contrast, complete blockade of bradykinin-induced relaxation was obtained when we combined the nonselective BK Ca and intermediate-conductance (IK Ca ) Ca 2ϩ -dependent K ϩ channel blocker charybdotoxin and apamin with hydroxocobalamin. Charybdotoxin plus apamin alone were without effect. Inhibition of inwardly rectifying K ϩ channels (K IR ) and Na ϩ /K ϩ -ATPase (with BaCl 2 and ouabain, respectively) shifted the bradykinin concentration-response curve 10-fold to the right but did not exert an additional effect in the presence of hydroxocobalamin. In conclusion, bradykinin-induced relaxation in HCMAs depends on (1) the activation of guanylyl cyclase, K IR , and Na ϩ /K ϩ -ATPase by NO and (2) IK Ca and SK Ca channels. The latter are activated by a factor other than NO. This factor is not a cytochrome P450 epoxygenase product or H 2 O 2 , nor does it depend on gap junctions or BK Ca channels. Key Words: bradykinin Ⅲ arteries Ⅲ endothelium-derived factors Ⅲ nitric oxide E ndothelium-dependent relaxation induced by bradykinin cannot fully be attributed to the release of nitric oxide (NO). In resistance-size vessels, a large proportion of endothelium-derived relaxation involves the release of endothelium-derived hyperpolarizing factors (EDHFs). 1 Putative EDHF candidates are prostacyclin, S-nitrosothiols, K ϩ , cytochrome P450 products of arachidonic acid (epoxyeicosatrienoic acids [EETs]), and H 2 O 2 , 2-8 and EDHF-dependent responses have been reported to involve large-, intermediate-, and/or small-conductance Ca 2ϩ -activated K ϩ channels (BK Ca , IK Ca , and SK Ca, respectively), inwardly rectifying K ϩ (K IR ) channels, Na ϩ /K ϩ -ATPase, and gap junctions. 4,5,8 -10 Busse et al 9 recently summarized all currently available data on EDHF and proposed that EDHF-mediated relaxation (ie, relaxation observed in the absence of NO) depends on the activation of endothelial IK Ca and SK Ca channels. 4 Such activation results in the release of K ϩ into the myoendothelial spac...

Developmental acceleration of bradykinin-dependent relaxation by prenatal chronic hypoxia impedes normal development after birth

“…Although such differences in how sGC inhibition influences bradykinin vs. ProliNO relaxation are unlikely, they may reflect nonspecific effects of ODQ that attenuate the bradykinin-induced vasodilation pathway at points upstream of sGC activation (6,29,80,85). The differences in the actions of ODQ also suggest that while a major portion of bradykinin-induced relaxation is through cGMP generation, its mechanism of action may also involve NO degradation through phosphodiesterases or NO-independent pathways (6,85). The ProliNO data further illustrate that bradykinin does not maximally activate relaxation pathways and that there is substantial NO-sensitive and sGC-insensitive reserve.…”

Endothelium-Derived Epoxyeicosatrienoic Acids and Vascular Function

“…The latter observation is, however, controversial, and the bradykinin-induced relaxation of human small coronary arteries (diameter Ϸ300 m) has also been recently described as depending on the activation of guanylyl cyclase, inwardly rectifying K ϩ channels, and the Na ϩ -K ϩ ATPase by NO, as well as on the activation of small and intermediate conductance K Ca channels by a factor that is not a CYP epoxygenase product or H 2 O 2 . 21 Given the latter observations together with the consideration that EETs are rapidly metabolized by the sEH and the fact that the CYPdependent EDHF-mediated relaxation of porcine coronary arteries is also sensitive to the combination of charybdotoxin and apamin, it seemed that EETs may exert additional functions within endothelial cells that ultimately result in the activation of small and intermediate conductance K Ca channels. The effects of EETs on small and intermediate conductance K Ca channels need not be direct, and there is evidence indicating that endogenously generated EETs can activate K Ca channels by activating membrane-associated second messengers.…”

“…21 Given the latter observations together with the consideration that EETs are rapidly metabolized by the sEH and the fact that the CYPdependent EDHF-mediated relaxation of porcine coronary arteries is also sensitive to the combination of charybdotoxin and apamin, it seemed that EETs may exert additional functions within endothelial cells that ultimately result in the activation of small and intermediate conductance K Ca channels. The effects of EETs on small and intermediate conductance K Ca channels need not be direct, and there is evidence indicating that endogenously generated EETs can activate K Ca channels by activating membrane-associated second messengers.…”

Selective Angiotensin-Converting Enzyme C-Domain Inhibition Is Sufficient to Prevent Angiotensin I–Induced Vasoconstriction

“…15 HCMAs rather than large human coronary arteries were used because only the former relax to bradykinin. 16 PCMAs were used in the bradykinin studies involving RXPA380 and RXP407 because of the limited availability of these drugs. All baths contained Krebs bicarbonate solution at 37°C and were aerated with 95% O 2 and 5% CO 2 .…”